Recently, an aqueous urethane resin composition has been investigated to be applied to a film or a sheet for optical application. Specifically, examples of the optical application include a liquid crystal display, a touch panel, and the like. In general, a display device such as a liquid crystal display has a configuration in which a plurality of optical films having various functions are laminated for displaying a clear image, and examples of such an optical film include an antireflection film, a retardation film, a prism lens sheet, and the like.
A polyester film, in particular, a polyethylene terephthalate (PET) film is used as a substrate of such an optical film from the viewpoint of excellent optical properties, mechanical strength, and durability. In addition, in the optical application, a prism sheet is prepared by forming a hard coat layer by applying an active energy ray curable composition onto the surface of the polyester film and curing the active energy ray curable composition or by disposing a layer which is formed by casting an active energy ray curable composition, but since the polyester film has a high crystallinity there is a problem that adhesiveness with respect to the a cured coating film of the active energy ray curable composition is deteriorated.
As a method for improving adhesiveness between a polyester film and a cured coating film of an active energy ray curable composition, a method in which a primer layer formed of an acrylic resin is disposed between the polyester film which is a substrate and the cured coating film of the active energy ray curable composition has been proposed (for example, refer to PTL 1). However, even when the primer layer formed of the acrylic resin is disposed, adhesiveness between the polyester film and the cured coating film of the active energy ray curable composition is not sufficient.
Therefore, a material which is able to be used in the primer layer for providing sufficient adhesiveness between the polyester film and the cured coating film of the active energy ray curable composition has been required.